# 80. Remove Duplicates from Sorted Array II

Given a sorted array *nums*, remove the duplicates [**in-place**](https://en.wikipedia.org/wiki/In-place_algorithm) such that duplicates appeared at most *twice* and return the new length.

Do not allocate extra space for another array, you must do this by **modifying the input array** [**in-place**](https://en.wikipedia.org/wiki/In-place_algorithm) with O(1) extra memory.

**Example 1:**

```
Given nums = [1,1,1,2,2,3],

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3 respectively.

It doesn't matter what you leave beyond the returned length.
```

**Example 2:**

```
Given nums = [0,0,1,1,1,1,2,3,3],

Your function should return length = 7, with the first seven elements of nums being modified to 0, 0, 1, 1, 2, 3 and 3 respectively.

It doesn't matter what values are set beyond the returned length.
```

**Clarification:**

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by **reference**, which means modification to the input array will be known to the caller as well.

Internally you can think of this:

```
// nums is passed in by reference. (i.e., without making a copy)
int len = removeDuplicates(nums);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}
```

```cpp
// Two pointer method
int removeDuplicates(vector<int>& nums) { // time: O(n); space: O(1)
    int n = nums.size();
    if (n <= 2) return n;
    int pos = 2;
    for (int i = 2; i < n; ++i) {
        if (nums[pos - 2] != nums[i])
            nums[pos++] = nums[i];
    }
    return pos;
}
```

{% content-ref url="26.-remove-duplicates-from-sorted-array" %}
[26.-remove-duplicates-from-sorted-array](https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/array/26.-remove-duplicates-from-sorted-array)
{% endcontent-ref %}
